Recent progress in genetics has identified a new class of RNA molecules called microRNAs (miRNA) involved in gene regulation. miRNAs are single-stranded RNA molecules of ~22 nucleotides complementary to a site in the 3'untranslated region (UTR) of mRNAs. The annealing of the miRNA to the mRNA inhibits protein translation and sometimes facilitates cleavage of the mRNA. This regulation adds an unexpected layer of complexity to the classic "linear" concept of DNA->mRNA->protein. Fast paced progress in the recent years showed the importance of miRNA in regulating neuronal and immune functions. In the CNS, miRNAs have been implicated in synaptic development and memory formation. We have found that constitutive knock out of miR-155 (miR-155-/-) increases the infract area in the mouse middle cerebral artery occlusion/reperfusion (MCAO/R) model by ~50%. However, miR-155 is expressed in the CNS in by at least astrocytes and microglia. The constitutive knock out of miR-155-/- makes it impossible to determine which cell type is responsible for the substantial increase in infarct area. We therefore wish to generate a conditional knock out model using the Cre/loxP approach. Using this well established approach we will be able to cross the floxed miR-155 (miR-155fl/fl) with readily available Cre-driver mice for astrocytes and microglia to generate cell specific knock out mice. The long-term goal of this project is to generate conditional knock outs of miR-155 to investigate the role of cell-specific miR-155 in CNS injury such as ischemic injury. We believe that the molecular mechanisms identified in subsequent experiments using this model may indentify new pathways for therapeutic intervention in CNS injuries such as stroke. PUBLIC HEALTH RELEVANCE: The broad, long-term goal of this project is to understand the role of miR-155 in the activation of astrocytes microglial cells. We believe that the signal transduction mechanisms identified through our experiments may constitute new targets for therapeutic intervention in CNS injuries associated with glial activation such as trauma, multiple sclerosis or stroke.